The fastest way to change the theme of your Ionic app is to set a new value for primary, since Ionic uses the primary color by default to style most components. Colors can be removed from the map if they aren’t being used, but primary should not be removed.

Custom Colors

Note: Adding a color will generate CSS styles for all Ionic components. This inflates the size of your CSS file and can slow down your app. If you only need to use the color in a few places, we recommend adding a new Sass variable for it.

You can customize colors even further by supplying a base and contrast property: